An engine control module of an internal combustion engine controls the mixture of fuel and air supplied to combustion chambers within cylinders of the engine. After the air/fuel mixture is ignited, combustion takes place and the combustion gases exit the combustion chambers through exhaust valves. The combustion gases are directed by an exhaust manifold to a catalytic converter and/or other components of exhaust aftertreatment systems.
Manufacturers of internal combustion engines, particularly diesel engines, are presented with the challenging task of complying with current and future emission standards for the release of oxides of nitrogen, particularly nitrogen monoxide, as well as unburned and partially oxidized hydrocarbons, carbon monoxide, particulates and other combustion byproducts. In order to reduce the emissions of internal combustion engines, an exhaust aftertreatment system is used to meet emissions criteria for the exhaust gas.
Exhaust gas aftertreatment systems typically include one or more aftertreatment devices, such as particulate filters, oxidation catalysts, selective catalyst reduction devices, NOx traps, mixing elements and urea/hydrocarbon injectors. The temperature of the exhaust gas flowing in the system can affect the performance of some exhaust system components. For example, an oxidation catalyst may take a selected amount of time after the engine starts to reach its “light-off” or operating temperature. A particulate filter may rely directly on an oxidation catalyst generated exotherm to elevate and maintain exhaust gas temperature to a selected value at which regeneration (i.e., burning of particulates accumulated in the filter) takes place. Thus, the exhaust gas flowing from exhaust components upstream of the particulate filter can affect performance of the filter. Accordingly, if components are not performing efficiently, an indication of the specific cause of reduced performance may be useful in servicing the system. In some cases, information provided to the user or technician is not specific enough to allow for accurate determination of performance deficiencies during service.